1. Field of the Invention
The present invention relates to a machine tool having oil pans for introducing chips generated by the machining of a workpiece onto a chip conveyer disposed within a trough formed in a bed. Particularly, the invention relates to a machine tool which is designed so that chips generated by the machining of a workpiece can assuredly be introduced onto a chip conveyer through oil pans.
2. Description of Related Art
An exemplary machine tool of the aforesaid type is a horizontal machining center 50 as shown in FIGS. 7 and 8. As shown, the horizontal machining center 50 includes a bed 51 having a center trough 52 formed in a widthwise middle portion thereof, a table 53 movable longitudinally of the bed 51 on the bed 51 and pivotally supporting a pallet P carrying a workpiece, an automatic pallet changer 54 for automatically exchanging a workpiece-carrying pallet P located in a preparation region α adjacent to one longitudinal end of the bed 51 and the workpiece-carrying pallet P mounted on the table 53 in a machining region β, and a spindle head 55 disposed at the other longitudinal end of the bed 51 and movable transversely and vertically of the bed 51. In FIG. 7, the horizontal machining center 50 is illustrated with the spindle head 55 removed.
The automatic pallet changer 54 includes a pair of pallet exchange arms 54a pivotal about a pivot point located on a boundary between the preparation region α and the machining region β, and a separation plate 54b separating the preparation region α and the machining region β. When the pallet P mounted on the table 53 is changed, the pallet exchange arms 54a are pivoted together with the separation plate 54b. 
Oil pans 56 for introducing chips generated by the machining of the workpiece into the center trough 52 are provided on widthwise opposite portions of the bed 51 in the machining region β as extending obliquely upward outwardly from widthwise opposite sides of the center trough 52. A chip conveyer 57 is provided in the center trough 52 as extending from the preparation region α toward the spindle head 55 through the machining region β for conveying chips removed from the workpiece and the pallet into the center trough 52 by an operator in the preparation region α and chips introduced into the center trough 52 through the oil pans 56 away from the preparation region α and the machining region β.
A ball screw 58 of a reciprocal drive mechanism for the table 53 is supported rotatably at a fixed position above the chip conveyer 57 in the center trough 52. A chevron-shaped extendible cover (not shown) is attached to the table 53 as covering the ball screw 58.
In the aforesaid horizontal machining center 50, the oil pans 56 each have a reduced inclination angle as shown in FIG. 8 for prevention of interference with the spindle head 55 to be moved transversely of the bed 51 during the machining of the workpiece and interference with the separation plate 54b to be pivoted for the exchange of the workpiece-carrying pallets P. With the reduced inclination angle of the oil pans 56, however, the chips generated by the machining of the workpiece are liable to remain on slant surfaces of the oil pans 56, making it difficult to assuredly introduce the chips onto the chip conveyer 57 in the center trough 52.
Since the chip conveyer 57 extends to the preparation region α for transporting the chips away from the preparation region α in the horizontal machining center 50, the ball screw 58 of the reciprocal drive mechanism for the table 53 is located above the chip conveyer 57 within the center trough 52. Therefore, the center trough 52 should have a greater depth, so that the rigidity of the bed 51 is reduced.
It is therefore an object of the present invention to provide a machine tool which is designed so that chips generated by the machining of a workpiece can assuredly be introduced onto a chip conveyer disposed in a trough of a bed through oil pans. It is another object of the present invention to provide a machine tool which is designed so that a center trough has a minimum depth even if a ball screw is provided in the center trough.